IWC Schaffhausen Aquatimer Split Minute Chronograph Mode D'emploi page 30

Determining bracelet length
Place the watch with the bracelet open around your wrist
and estimate the number of surplus bracelet links that
you can now remove from the bracelet (as described
above).
If you need to shorten the bracelet by several links, you
should remove the same number of links from each half
of the bracelet, if possible, to ensure that the clasp can
be worn more or less at the centre of the wrist. To enable
you to adapt the bracelet as accurately as possible to
the size of your wrist, we have included an extra-long
bracelet link in the clasp. Your bracelet is shortened by
an intermediate amount by omitting this bracelet link,
and finer adjustment to the length of the bracelet can be
made in this way.
Keep the surplus links and the separating tools safely for
use in subsequent adjustments.